Hypothalamic hamartoma (HH) is a rare benign brain tumor located near the hypothalamus. It usually straddles the optic nerve, making removal extremely difficult or impossible. The lesions can be found using Magnetic Resonance Imaging (MRI). Although little is known about the origin of such tumors, some research suggests that hypothalamic hamartomas may develop during the sixth or seventh week of gestation.

Epileptic syndrome associated with HH characteristically begins in infancy with gelastic (laughing) seizures. Early childhood psychomotor development is usually normal. The episodes of laughter are brief, relatively frequent and mechanical in nature. They so much resemble natural laughter that parents and physicians often do not recognize that the child is experiencing a seizure, thus leading to a delay in diagnosis of epilepsy and the hypothalamic hamartoma.

In later childhood, typically between the ages of 4 and 10, the disorder enters a more ominous phase. Instead of the pleasant infectious giggle, the laughing seizures become longer and more severe, taking on less natural sounds. Features of secondary generalized epilepsy may appear. Multiple seizure patterns (including tonic, atonic and tonic-clonic seizures) and progressive cognitive impairment can also occur. Also at this later stage, the child burdened by the HH may start to display bouts of extreme rages, poor social adjustment, and often precocious (early) puberty.

In some cases anticonvulsants may help to alleviate some occurances of epileptic seizures. However, more commonly there is little or no help in controlling the frequency or duration of the laughing seizures. As a result, most children with this condition suffer multiple gelastic seizures daily. The frequency of these seizures and the subsequent disruption to the brain, often makes deterioration of the child's mental state unavoidable. Regression in the level of intellect sometimes leads to mental retardation (some HH children display signs of autism) and the rages may become so severe that institutionalization may be necessary.

It was A. Trousseau who, in 1873, first suggested that episodes involving spontaneous, unprovoked and apparently uncontrollable laughter might indeed be an an epileptic phenomenon. But HH with gelastic epilepsy is rare and generally understudied. Ames and Enderstein (1980) suggest only around 100 cases have been reported since Trousseau's discovery, however a review of the relevant literature (and the number of HH cases that have come to the attention to this internet support group) suggests this could be a very conservative estimate.  In the year 1957 alone, Druckman and Chao described 11 patients for whom they believed laughter was an epileptic manifestation. In the same year Daly and Mulder were the first to coin the term "gelastic epilepsy" in describing two patients in who laughter formed an integral part of their seizure pattern. In reviewing a selected group of patients with complex epilepsies, Chen and Forster (1973) found only 10 with gelastic epilepsy - an incidence of 1 in 500. However, the truth is no-one really knows the true extent of this condition.